FORM
 
AFFIRMATIVE (+) 
S
had
V3
I had
worked /
written
We had
worked /
written
You had
worked /
written
They had
worked /
written
He had
worked /
written
She had
worked /
written
It had
worked /
written

Short forms: 
had = 'd
I had worked = I'd worked
NOTE!
" 'd " may be used in different situations:
 
1. 'd V3 = had V3 — Past Perfect
E.g. He'd finished his homework by six o'clock. = He had finished his homework by six o'clock.
 
2. 'd V = would V
E.g. I'd like to go to the cinema. = I would like to go to the cinema. 
 
3. 'd better V = had better V
E.g. You have an interview tomorrow at 8 o'clock. You'd better go to bed early. = You had better go to bed early.
NEGATIVE (-)
S
had
not
V3
I had not
worked /
written
We had not
worked /
written
You had not
worked /
written
They had not
worked /
written
He had not
worked /
written
She had not
worked /
written
It had not
worked /
written
 
Short forms:
 
had not = hadn't
I had not worked. = I hadn't worked.
  
***
S — Subject of the sentence. E.g. I, we, you, they, he, she, it, Mary, John, my friends, etc.
V3 — Verb in the 3rd form (Past Participle). E.g. written, gone, listened, etc.
Revise irregular verbs here and how to add "ed" to regular verbs here.